Process for obtaining multiple photographic positive images by diffusiontransfer



United States Patent 3,174,859 PROCESS FOR OBTAINHNG MULTIPLE PHOTO- GRAPEHC POSITIVE IMAGES BY DIFFUSION- TRANSFER Albert Emiel Van Hoof, Berchem-Antwerp, and Rene Maurice Hart and Jozef Frans Willems, Wilrijk-Ant= werp, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsel-Antwerp, Belgium, a Belgian company No Drawing. Filed Sept. 23, 1960, Ser. No. 57,903 Claims priority, applicatizon l fetherlands, Sept. 24, 1959,

7 Claims. (Cl. 96--29) The present invention relates to the manufacture of a number of images by starting from one same negative according to the silver complex diffusion-transfer process.

According to the general principle of the diffusiontransfer process described in U.S. Patent 2,352,014 and in Photography, Its Materials and Processes, by C. B. Neblette, th edition, pages 234-244, an image-wise exposed photographic silver halide emulsion layer (negative) is brought into contact with another non-lightsensitive receiving layer (positive), containing development nuclei, and developed in a developer containing a solvent for the silver halide. During the formation of the image in the emulsion layer sufi'icient amounts of silver halide are complexed on the non-exposed parts of the negative which by diffusion-transfer in the non-lightsensitive receiving layer form a positive as a result of the reducing action of the developer which is catalyzed by the development nuclei present in the receiving layer.

The meaning of the terms negative and positive as used in this description is relative; if the emulsion layer is exposed to a negative image, a direct negative will be produced in the reception layer; if the emulsion layer is exposed to a positive image a direct positive will be obtained in the reception layer.

This principle of diffusion-transfer process is applied in many offices for quickly printing letters, documents and drawings. In general, only one usable positive print can be obtained with the printing apparatus suitable for this purpose, although the quantity of silver used therefor represents only a small part of the available amount of silver halide in the unexposed parts of the silver halide emulsion layer, so that theoretically there is the possibility of making several prints of one same negative.

It is, however, necessary to obtain sometimes as quickly and as inexpensive as possible several prints of the same original. If, however, one tries to make even a second copy of the same second negative by bringing the latter into contact with a second receiving layer and according to the above-described process to lead it through a special developing solution, a quite unsatisfactory result is attained.

Yet, it is known to make several prints by means of one same negative by using in the developing solution a decreasing concentration of solvent for the silver halide (Sievers, A. 1., Phot. Soc. of America, Technical Quarterly, May 1955, pp. 75-78).

It has also been proposed to add to the developing bath besides the solvent for silver halide fixing accelerators, desensitizers for the latent image and plasticizers for gelatin (U.S.P. 2,834,676).

All these means, however, do not satisfy and give rather faint positive images of poor intensity whereby the number of good positive prints is restricted to at most 4 or 5.

It is also known to make a number of positive prints from a single negative by slowing down the complexing of the unexposed silver halide during processing by adding to the receiving material or to the bath compounds which slowly give halogen ions, or by causing this complexing 3,174,35? Patented Mar. 23, 1955 "ice to proceed in the presence of an excess of alkali halide (Belgian Patent 545.312).

Now has been found that according to the silver complex diffusion-transfer process, a number of positive prints with more intense tone can be made from a single negative by adding to one or more layers of the receiving material water-soluble basic polymers.

Suitable basic polymers are e.g.:

(1) Polyvinyl amines (e.g. as described in the Belgian patent specification 540,976 and the British patent specification 830,189) and its substituted derivatives such as N-dialkylopolyvinylamines etc.

(2) Polyalkylene imines such as polyethylene imine and its substituted derivatives as disclosed in U.S. application Serial No. 46,879, commonly owned with the present application, and in British Patent No. 755,478.

Unless the basic polymer is already in the form of its salt, it is neutralized, as with hydrochloric acid, to form the corresponding salt.

The compounds used according to the present invention can be incorporated into several layers of the receiving material as far, however, as their presence is compatible with the elements from which such respective layers are composed. In the circumstances, they can be added to an auxiliary layer, a baryta-layer or even to the paper itself, although preferably the applied process consists in incorporating them into the nuclei-containing layer. It was further observed that the favorable effect obtained with the basic polymers depends on the kind of nuclei used.

Suitable developing nuclei which act as reducing nuclei for the complexed silver halide are i.e. colloidal silver and sulphur, colloidal metal sulfide such as copper, nickel, tin, silver and zinc sulfide. Other compounds do not serve as nuclei but are able to form such nuclei by interaction with the diffusing silver complexes, either by reduction such as in the case of stannous chloride or by the formation of difiiculty soluble compounds with sulfides or organic compounds which easily split 01f sulphur in the form of a bivalent ion such as in the case of thiosinamine.

In order to obtain an as high as possible covering, it is advisable to apply the addition, according to the invention, to development nuclei which must not be too small. This can be obtained by forming the colloidally dispersed nuclei in a medium which contains only little protective colloid.

Although it cannot be explained with certainty how a more intense tone is obtained with these polymers in the receiving layer, it is supposed that the soluble silver halide complex diffuses from the negative emulsion layer to the positive and it precipitated therein in compact form by the basic polymer present. At the same time, the diffusion equilibrium would be shifted in favor of the positive.

A further intensification of the image tone is attained, by adding to one of the layers of the positive material minor amounts of anti-fogging agents such as phenyl mercapto tetrazole, benzotriazole, mercapto benzotriazole etc.

An advantage of the present invention consists therein that the usual developing baths and apparatus for the silver complex diifusion transfer process can be used without any modification. in an apparatus containing the usual developing solution prints can be made according to the system of one copy per negative such as described in the U.S. patent specification 2,352,014 as well as a number of prints of one same negative according to the invention.

The silver halide emulsions which are suitable for applying the new method comprises silver chloro-bromide emulsions, silver bromide emulsions containing silver chloride and silver chloride emulsions which all of them can also contain small amounts of silver iodide. However, for obtaining a quick diffusion-transfer of the complexed silver halide preferably emulsions are used which mainly contain silver chloride. If, however, exposure times as short as possible are wanted, it is advantageous to use sensitive silver bromide emulsions which contain a small amount of silver chloride.

It has further been stated that when making a number of prints the first print adheres sutficiently strongly to the negative. In the following prints, however, the adherence gradually decreases, so that the last prints are spotted by lack of intimate contact between the negative and positive prints. The adherence between positive and negative must not be raised in such a way that both can only hardly be separated from each other. The exact strength of adherence can be obtained if to the positive and/or to the negative material, but preferably to positive and negative materials, a layer of a hydrophilic watersoluble high-molecular substance or of a mixture of such substances is applied. These substances or colloid binding agents can be of natural and half-synthetic, as well as of fully synthetic kind. As suitable binding agents can be used arabic gum, tragacanth gum, pectine, cellulose derivatives such as methyl cellulose, hydroxyl cellulose and carboxymethyl cellulose, polyvinyl alcohol, party hydrolyzed polyvinyl esters, such as polyvinyl acetate, polyvinyl pyrrolidone, dimethylhydantoine-formaldehyde resins etc. i

It has also been stated that hydrophilic high-molecular substances can successfully be added to the image-receiving layer which for instance contains gelatin as binding agent in order to keep the adherence of the positive to the negative on a favorable level. Simultaneously, these high-molecular substances can bring along an improvement of the intensity of the positive probably in consequence of an increased reaction power of the nucleicontaining layer thus obtained.

In this case, the positive material can be made in a very simple way since then only one layer must be applied to the support, e.g. paper.

It was observed that the tanning of the colloid layer of the positive as well as of the negative exerts an unfavorable infiuence on obtaining a uniform and sufliciently high density on the positive. The addition of tanning agents to colloid layers indeed reduces the permeability of the latter and makes difficult the diffusiontransfer of the complexed silver salts of the light-sensitive layer to the receiving layer. In the circumstances it was stated that the addition of an anti-hardening or softening agent to at least one of the layers of the negative or of the positive is very favorable for obtaining prints with a higher density.

There are different products which are known as softening or anti-hardening agents, such as urea, water-soluble thiocyanates, nitrates and halides such as potassium thiocyanate, potassium nitrate, sodium nitrate, potassium iodide, barium chloride, calcium chloride and magnesium chloride, ammonium salts, sodium salicylate, formarnide, dimethyl formamide, ethylene chlorohydrin, chloral hydrate and alpha-naphthalene sodium sulfonate. The best results, however, were attained with urea. This product can be added in amounts of 5 to 80% on the weight of binding agent present in the negative and/or of the positive layers.

In order to give the different prints obtained according to the present invention a better appearance and a longer life-time, compounds which counteract the staining of the material, such as for instance organic halogen containing phosphonic acid and phosphoric acid esters de- 4 Example 1 A negative material is prepared by coating onto a 200 g./m. cardboard paper a contrasty silver chloride emulsion whereto per kg. of emulsion 20 g. of urea and 30 g. of rice starch are added. Next, a 1% aqueous solution of carboxymethyl cellulose is applied to this emulsion layer. A positive receiving material is prepared by coating onto a paper of an appropriate quality a nuclei containing layer from the following suspension:

G. Gelatin 40 Colloidal cobalt sulphide 0.23 Sodium thiosulphate 3 Polyvinylamine hydrochloride 2.5 Phenylmercaptotetrazole 0.1

Water to 1000 To this positive receiving layer a second layer is applied from a 2% aqueous solution of carboxymethyl cellulose. A sheet of a negative material is exposed to an image. In the usual way, it is pressed into contact with a sheet of positive material in the presence of the following developer:

' G. Sodium sulphite (anhydrous) 65 Hydroquinone 14 l-phenyl-3-pyrazolidone 1 Sodium hydroxide 11 Potassium bromide 1 Water to 1000 cm.

After 5 seconds the two sheets are separated and the negative sheet is pressed into contact with a second sheet of positive material from which it is likewise separated after 5 seconds. By repeating this process, 10 sharp prints can be prepared with one and the same negative.

Example 2 Analogously to Example 1, a negative material is prepared. Next, a positive receiving layer is prepared by coating first on a paper of an appropriate quality a nucleicontaining layer from the following suspension:

' G. Gelatin 40 Colloidal silver sulphide 0.7 Sodium thiosulphate (anhydrous) 4 Polyethylene-imine hydrochloride 2 Benzotriazole 0.1

Water to 1000 cm.

Next, a 2% aqueous solution of carboxymethyl cellulose is applied to this nuclei-containing layer. In the same way and with the same developer solution as mentioned in Example 1, 10 sharp prints can be obtained with one and the same negative.

Example 3 Example 4 Analogously to Example 1 a ne ative material is prepared. Next, a positive material according to that of Example 2 is used, but whereto 10 g. of urea per litre of nuclei-containing layer composition are added. By repeating the development as mentioned in Example 1, 10 sharp prints can be obtained from one and the same negative.

wan R Example 5 Similar favorable results as described in Example 2 can be attained by replacing in the suspension composition of that example 0.7 g. of colloidal silver sulphide by 0.2 g. of colloidal zinc sulphide.

We claim:

1. A process for obtaining multiple copies from an exposed silver halide emulsion layer, which comprises contacting said emulsion layer With a first receiving layer containing development nuclei, a binding agent and a neutralized polyvinyl amine polymer in the presence of silver halide developer and a silver halide solvent, separating the layers and recontacting the silver halide emulsion layer With another of said receiving layers in the presence of said silver halide developer and a silver halide solvent.

2. A process for obtaining multiple copies from an exposed silver halide emulsion layer, which comprises contacting said emulsion layer with a first receiving layer containing development nuclei, a binding agent, urea and a neutralized polyvinyl amine polymer in the present of a silver halide developer and a silver halide solvent, separating the layers and recontacting the silver halide emulsion layer with another of said receiving layers in the presence of said silver halide developer and a silver halide solvent.

3. The precess of claim 1 wherein said receiving layer contains about 5-80% by Weight of said binding agent of a softening agent for said binding agent.

4. The process of claim 1 wherein at least one of said emulsion layer and said receiving layers bears a super- 6 posed layer of a Water-soluble high molecular weight hydrophilic colloid.

5. The process of claim 1 wherein said neutralized polyvinyl amine polymer is water soluble.

6. The process of claim 1 wherein said emulsion layer contains a binding agent and about 580% by Weight of said binding agent of a softening agent for said binding agent.

7. The process of claim 2 wherein said neutralized polyvinyl amine polymer is Water soluble.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Glafkides: Photographic Chemistry, Fountain Press,

London (1958), pp. -157. 

1. A PROCESS FOR OBTAINING MULTIPLE COPIES FROM AN EXPOSED SILVER HALIDE EMULSION LAYER, WHICH COMPRISES CONTACTING SAID EMULSION LAYER WITH A FIRST RECEIVING LAYER CONTAINING DEVELOPMENT NUCELI, A BINDING AGENT AND A NEUTRALIZED POLYVINYL AMINE POLYMER IN THE PRESENCE OF SILVER HALIDE DEVELOPER AND A SILVER HALIDE SOLVENT, SEPARATING THE LAYERS AND RECONTACTING THE SILVER HALIDE EMULSION LAYER WITH ANOTHER OF SAID RECEIVING LAYRS IN THE PRESENCE OF SAID SILVER HALIDE DEVELOPER AND A SILVER HALIDE SOLVENT. 